Suppression of ultraviolet light (UVL)-induced squamous cell carcinomas in skin of hairless mice by dietary antioxidants is well established. However, the mode of action of antioxidants and the mechanism of UVL-induced skin carcinogenesis are not clearly understood. Recently, in Chinese hamster cells, reversal of UVL-induced cytotoxicity by certain antioxidants was demonstrated for the first time in our laboratory. This proposal is designed to use several cell lines of different animal origin to characterize this antioxidant-mediated reversal of UVL-induced cytotoxicity. Subsequently, this property of antioxidants will be established as a model system for studying the prophylactic role of antioxidants in actinic carcinogenesis as well as the mechanism of UVL-induced skin carcinogenesis. Using a C3H/1OT 1/2 CL8 mouse cell line which others have shown to be transformed by exposure to UVL and subsequent promotion by tetradecanoyl phorbol acetate (TPA), antioxidants will be examined for their possible role in inhibiting UVL-induced transformation. Studies will also be initiated to determine if cytotoxicity induced by chemical carcinogens may be reversed by antioxidants.